iis 7.5 – Protect static file on Asp Net Classic Mode with Forms Authentication

i’m struggling to resolve this issue since yesterday.

I have a site (framework 4.0), hosted in a Windows Server with IIS 7.5 in Classic Mode.
Unfortunately i can’t changed this to Integrated Mode.

I need to protect files contained in a folder.

Only authenticated user (with forms authentication) have to access to them.
anonymous user not.

I tried to protect folder in this way in webconfig:

<location path="Riservata/Files">
          <deny users="?" />

But i can access to these files (pdf), direct.
Instead i want to a redirect to the loginpage.

Someone can help me?